With the development of mobile communications technologies, great changes take place in people's production and life. A first-generation communications system implements a mobile two-way call by using an analog technology and a frequency division multiple access technology. By using a digital time division multiple access technology and a code division multiple access technology, a second-generation communications system improves call quality in the first-generation communications system and implements low-speed data transmission. A third-generation communications system and a fourth-generation communications system that subsequently appear not only improve call quality of a voice service, but also improve a data transmission speed.
In the third-generation communications system and the fourth-generation communications system, a multiple-input multiple-output (MIMO) technology is used.
A basic feature of the MIMO technology is using multiple transmit antennas and multiple receive antennas. Specifically, in the MIMO technology, multipath wireless communication, transmission, and receiving are regarded as an entirety. One manner is increasing a spatial dimension of data multiplexing, so that multiple portions of data space are multiplexed to a same time frequency resource. Another manner is sending same data on multiple transmit antennas and/or receiving same data by using multiple receive antennas, to obtain a control diversity gain. In this way, the MIMO technology increases a channel capacity without increasing bandwidth, thereby achieving a high communication capacity and high spectrum resource utilization.
However, the channel capacity linearly increases with an increase in an antenna number. To meet a requirement of the MIMO technology, a quantity of antennas configured on a terminal device increases from one antenna to four antennas or even more. Because the terminal device side transmits or receives data by using multiple antennas, compared with single input single output (SISO), not only calculation complexity increases when a quantity of channels used for transmitting data is estimated, but also complexity of selecting, by a base station, a channel for performing data transmission with the terminal device accordingly increases because of an increase in a quantity of antennas on the terminal device side. How to obtain antenna information of a terminal device in a timely manner becomes a problem that needs to be resolved.